This invention relates to a diamond radiation detector. Diamond is well known as a potential radiation detector. Its advantages include high radiation hardness, high thermal conductivity, rigidity, and simplicity of the detector design. However, its application has not been as widespread as anticipated, because of a range of practical problems.
Polycrystalline diamond radiation detectors are currently being assessed for a range of applications including particle detectors for the large hadron collider (LHC). In this application, radiation hardness is paramount, but another requirement is good separation of signal from background noise. Based on the particular signal characteristics exhibited by polycrystalline diamond, application of this material requires a charge collection distance (CCD) of at least 250 μm. The 250 μm collection distance is achieved by using very high quality polycrystalline diamond layers about 500 μm thick, and an applied field of 1 V/μm, equivalent to a voltage of about 500 V. It is found that the CCD in polycrystalline CVD diamond is a roughly linear function of the applied field up to about 1 V/μm, when the signal saturates, i.e. the CCD no longer increases when the field is increased.
Measurements of the CCD of natural single crystal diamond as a function of applied field suggest that it does not saturate at 1 V/μm, but continues to rise to much higher fields (see, for example, Zhao. S. (1994), PhD Thesis ‘Characterization of the Electrical Properties of Polycrystalline Diamond Films’, The Ohio State University) offering one route to higher CCD values, although exacerbating the problems of using higher voltages. However, the maximum CCD reached with such crystals is reported to be about 40 μm at 2 V/μm applied electric field.
WO 01/96633 discloses a high purity single crystal diamond produced by chemical vapour deposition (CVD). The diamond has a high resistivity, a high breakdown voltage in the off state, high electron mobility and hole mobility and a high collection distance. The diamond is described as being useful in electronic applications, particularly as a detector element or switching element.